1. Field of the Invention
The present invention relates to simple methods for measuring the strength of a film and determining the quality of an object to be measured, the object having the film.
2. Description of the Related Art
For an electronic component having a film, such as an external electrode, on the surface, it is important for exhibiting stable performance to increase the strength of the film and prevent the separation of the film. If an electronic component is the object to be measured, there are a variety of known methods for determining the property constants of the film, structural parameters such as the film thickness, and the presence of cracks and separations. For example, Japanese Examined Patent Application Publication No. 7-9418 (published on Feb. 1, 1995) discloses a method using a spectrum ultrasonic microscope that can perform two-dimensional and quantitative measurement and detection on a surface of an object to be measured.
In the spectrum ultrasonic microscope, an impulse generator transmits pulse signals to a transmitting transducer, which then changes the frequency of the ultrasonic waves corresponding to the pulse signals and applies the ultrasonic waves to the object to be measured. Reflected waves from the object are received by a receiving transducer, transformed into electric signals, and output. Received and amplified electric signals are analyzed by a spectrum analyzer serving as a frequency analyzer and converted from analog to digital. In a computer, an obtained frequency distribution undergoes a feature subtraction process in a digital-operation unit, as programmed by an operator. A resulting frequency distribution is stored in a storage unit and displayed in an image output unit. An X-Y-stage-driving unit connected to a stage for mounting the object to be measured is X-Y scanned in synchronization with signals from the impulse generator.
According to this structure, acoustic waves are applied to the object at a constant incident angle. The data obtained by receiving the reflected waves enable the property constants of the object, structural parameters such as the film thickness, and the presence of cracks and separations to be two-dimensionally and quantitatively measured and detected on the surface of the object.
In the method described in Japanese Examined Patent Application Publication No. 7-9418, pressure waves having wideband frequency components are applied to the object at a constant angle. Pressure waves reflected from the object are then processed by a fast Fourier transform (FFT) method. As shown in FIG. 8, a frequency corresponding to a minimum intensity is detected. Thus, the film thickness and the presence or absence of the film separation can be detected, and state changes on the surface of the object can be determined.
In the method described above, a film and a base firmly bonded together can be distinguished from a film and a base sandwiching a middle layer made of a different material, or from a film and a base totally separated from each other. However, since a film weakly bonded to a base material (defective) and a film firmly bonded to a base (normal) are similarly indicated, they cannot be distinguished from one another and the bond strength of a film cannot be quantitatively determined in this method.